It has been held to be improper to ask a medical witness whether the person, whose sanity was in question, possessed sufficient capacity to make a will, or to transact business, as these are matters of law, depending on the nature of the business ([326]). In England such witnesses can only speak as to the state of mind, not as to the responsibility of a prisoner; this latter point is for the jury under the direction of the Judge ([327]). So, on the plea of insanity at the time of making a contract, the opinion of the medical man who gave the certificate on which the defendant was confined as insane at or about the time, is only evidence for the jury, who must judge of the grounds upon which it was formed ([328]).
In England, an expert cannot be asked, after being present at the whole trial, whether the defendant was insane, or whether the act complained of was an insane act, because these are questions for the jury and the witness must not be placed in the jury’s place; but he may be asked whether such and such appearances, proved by other witnesses, are in his judgment symptoms of insanity ([329]). The particular facts proven by other witnesses may be taken and the expert may be asked “assuming these facts to be true, do they in your judgment indicate insanity on the part of the defendant at the time the alleged act was committed?” ([330]). |126|
As a rule the Court should not allow an expert to give his opinion upon facts proved by a witness unless he has heard all the testimony of the witness, because the entire testimony may be necessary in order to enable him to form an opinion in regard to the subject matter of inquiry ([331]).
Where the facts are disputed, experts can only be questioned as to their opinion of a party’s sanity on a hypothetical case, or as to certain designated facts existing in the case supposing them to be true ([332]).
The mode in which this hypothetical question is to be put has been much considered. In England, in the celebrated Macnaghten case in answer to an inquiry of the House of Lords, whether “a medical man conversant with the disease of insanity, who never saw the prisoner previously to the trial, but who was present during the whole trial and the examination of the witnesses, can be asked his opinion as to the state of the prisoner’s mind at the time of the commission of the alleged crime; or his opinion whether the prisoner was conscious at the time of doing the act, that he was acting contrary to the law; or whether he was labouring under any and what delusion at the time?” The twelve judges replied, “We think the medical man, under the circumstances supposed, cannot in strictness be asked his opinion in the terms above stated, because each of these questions involves the determination of the facts deposed to, which it is for the jury to decide, and the questions are not mere questions upon a matter of science in which case such evidence is admissible. But where the facts are admitted or not disputed, and the question becomes substantially one of science only, it may be convenient to |127| allow the question to be put in that general form, though the same cannot be insisted on as a matter of right ([333]).”
In Massachusetts, Chief Justice Shaw said, “The proper question to be put to the professional witness is this—If the symptoms and indications testified to by the other witnesses are proved and if the jury are satisfied of the truth of them, whether in their opinion the party was insane, and what was the nature and character of that insanity; what state of mind did they indicate; and what they would expect would be the conduct of such person in any supposed circumstances?” ([334]).
In another well known case, the Judge said to the jury, “It is not the province of the expert to draw inferences of facts from the evidence, but simply to declare his opinion on a known, or hypothetical state of facts, and therefore the counsel on each side have put to the physicians such states of fact as they deem warranted by the evidence, and have taken their opinions thereon. If you consider any of these states of facts put to the medical witnesses are proved, then the opinions thereon are admissible evidence, to be weighed by you, otherwise their opinions are not applicable to the case” ([335]).
The opinions of both experts and non-experts should have weight according to their opportunities and qualifications for examination of the state of mind of the person whose sanity is in question. First of all will be the family, or the physician who has attended the patient through the disease which is supposed to have disabled his mind; next are those who, without special learning on the subject, have had the best opportunities for judging—the members of his family and those whose intimacy in the family, have given them opportunities of seeing the patient at all times and |128| noticing the alienation of his mind; and last, come those who only occasionally and at intervals have seen him, and whose chances of studying his moods have been small ([336]).
It has been held, in Massachusetts, that a physician who had not made insanity a special subject, and who, when consulted in such matters, always called in a specialist, is not competent to give an opinion on an hypothetical case put to him, unless he was the person’s attending physician; then his opinion is received, as it is his duty to make himself acquainted with the peculiarities, bodily and mental, of a person who is the subject of his care and advice ([337]). And where a physician had for more than thirty years been exclusively treating the insane, he was not permitted to testify, as an expert, to the mental capacity of a person—not previously insane—who was in the last stages of disease ([338]).
One not an expert may give an opinion, founded on observation, as to whether a person is sane or insane, notwithstanding the general rule, that persons not medical men cannot give their opinions as to the existence, nature or extent of disease in any one. The exception was first introduced in regard to the subscribing witnesses to a will, who were permitted to speak as to the testator’s state of mind; it has now been extended to all cases where the witness’ acquaintance with the party whose sanity is in dispute, or his means of observation, are sufficient to enable him to express his opinion as to the mental condition. The Courts of Massachusetts, Maine, New Hampshire and Texas, however, still adhere to the old rule and admit the evidence of non-experts only in cases of wills ([339]).